Method of detecting the movement of heat in a subterranean hydrocarbon bearing formation during a thermal recovery process



Dec. 16, 1969 GILCHRIST ETA!- 3,483,730

METHOD OF DETECTING THE MOVEMENT OF HEAT IN A SUBTERRANEAN HYDROCARBON BEARING FORMATION DURING A THERMAL RECOVERY PROCESS Filed June 21, 1967 5000 .BWAS $754M Q 25 6000 BWAJ JTE'AMG 26 xvo 072-141 1 0 7 iNVEN T ORS Q K E414 ATTORNE Y nited States Patent 0 ABSTRACT OF THE DISCLOSURE A method for determining areal invasion of heat in a thermal recovery process. The method includes the steps of instituting a heat movement in a hydrocarbon bearing formation and subsequently monitoring the changes in temperature of a portion of the over burden of the formation at a plurality of monitoring points laterally or i areally spaced apart from the point of initiation of the heat movement, with the changes in temperature indicating the extent of movement of the heat.

This invention relates to a method of detecting the movement of heat in a subterranean hydrocarbon bearing formation. More particularly, it relates to a method of determining areal invasion of heat in a thermal recovery process.

There are many subterranean hydrocarbon bearing formations which have been difficult and uneconomic to produce unless the hydrocarbon bearing formation is heat ed in some manner to reduce the viscosity of the hydro carbons, thereby permitting recovery from the formation.

There are many prior art examples of various thermal recovery processes. As for example, processes utilizing steam drives or cyclical injections of steam down the well bore and into the formation, which heating is continued until the temperature of a portion of the reservoir containing the hydrocarbon material is heated to the desired level, as is well known to those skilled in the art.

Another well known method for instituting a heat movement in a hydrocarbon bearing formation is the use of an in-situ combustion project where a heat front is moved from one point to another, as between two well bores drilled into the formation.

The use of steam and in-situ combustions has opened up a tremendous amount of heretofore unrecoverable oil at reasonable investment costs. However, experience has shown that there is a tendency to overheat an oil containing formation by over injection of steam or excessive combustion. In many instances, the reservoir is overheated because it is difficult to predict the size of the steam stimulation treatment or the combustion time required.

Various attempts have been made in the past to detect the movement of heat in a subterranean hydrocarbon bearing information, one of which includes the use of observation well bores, drilled between an injection well and a production Well, for example. In this instance, the observation Wells are drilled into the formation in the same manner as the injection or production wells. However, observation Wells are costly to drill and provide a single point (in a pattern) detection method. Down-hole temperature logs in producing wells and observation wells are costly to maintain and diificult to interpret. The cost of drilling a sufiicient number of observation Wells is economically prohibitive in most instances and in other instances when observation wells are drilled, the steam does not move in the direction of the observation well and its use is therefore limited.

3,483,730 Patented Dec. 16, 1969 'ice Another prior art method which has been suggested is the use of seismic methods. Here, the high temperature zone provides a measurable anomaly. However, this is not as reliable a technique and can be quite expensive in some instances.

Further, knowledge of the direction of heat movement is not only useful in controlling overheating of the formation, as described above, but such information may be used to direct the heat movement by opening or shutting wells or increasing or decreasing steam injection at different points, for example.

It is therefore an object of this invention to provide an improved method for detecting the movement of heat in a hydrocarbon bearing formation, which method is economical in operation and use, whereby information can be quickly and easily received concerning the movement of the heat front in the subterranean formation, which information may be of use in preventing the overheating of overburden and underburden or in controlling the direction of movement of the heat front, or the like.

It has been discovered that in shallow fields, where the hydrocarbon bearing formation lies no more than about 1,000 feet below the ground surface, and preferably about 100 feet to about 500 feet below the ground surface, there will be measurable changes in the temperatures of the overburden at the surface, which changes can be measured and which indicate the movement of the heat during a heat movement. In this connection, it has also been discovered that the heat produced in the hydrocarbon bearing formation during a heat movement, is transmitted upwardly through the overburden not merely by pure conduction, but rather by convection. That is, there is a movement of heated fluids upwardly through the overburden. While heat movement by conduction through overburden is relatively slow, heat movement via convection is much more rapid, and hence, permits the carrying out of the present invention.

Information concerning the direction of the heat movement is useful as stated above in not only preventing overheating of the formation, but in controlling the flow of the heat movement by opening additional wells and shutting in others or varying the steam input at various wells, or the like.

Briefly stated, this invention includes the steps of instituting a heat movement in the hydrocarbon bearing formation and monitoring the change in temperature of a portion of the overburden of said formation at a plurality of monitoring points laterally or areally spaced apart from the point of initiation of the heat movement as an indication of the extent of the movement of the heat. Preferably, the change in the temperature of the overburden near the ground surface is monitored at a plurality of points areally spaced apart from the point of initiation of the heat as an indication of the extent of areal movement of the heat.

This monitoring is conveniently and preferably carried out by contacting a plurality of thermocouples in heat exchanged relationship with the overburden (preferably the surface portion thereof), and reading out the variation in the electrical voltage produced by the thermocouples in response to changes in temperature of the overburden during the heat movement as indications of the movement of the heat.

The term surface ground has been used to define that portion of the overburden which lies adjacent to the surface of the earth. It is limited to that area not more than about 50 feet in depth and preferably much less, such as only a few feet, as for example, four feet. Shallow holes of this type may be easily drilled with conventional equipment at a minimum of cost.

In the preferred embodiment, small holes 4 to 8 inches in diameter are drilled about four feet in depth and the thermocouples installed near the bottom of the holes. The holes are then subsequently at least partially filled with a generally uniform conducting medium such as sand. The medium is then allowed to come to a temperature equilibrium with the adjacent surface ground. Readings are then taken of the electrical voltages produced by the thermocouples at convenient time intervals as an indication of the movement of the heat in the hydrocarbon bearing formation.

In certain embodiments of the method, the shallow holes can be drilled between two or more well bores which extend into the formation and the movement of heat between the well bores through the hydrocarbon bearing formation monitored in a similar fashion.

Reference to the drawing will further explain the invention wherein:

FIG. 1 is a plan view showing three well bores extending into a hydrocarbon bearing formation with a plurality of monitoring points spaced apart therebetween.

FIG. 2 is a schematic side elevation view in central section of a monitoring hole dug in the surface ground to a depth of approximately four feet, and showing the installation of a thermocouple therein.

In carrying out the present invention, the monitoring points are preferably in the form of a plurality of small shallow holes as shown in FIG. 2, which may be approximately 4 to 8 inches in diameter and extend approximately four feet deep into the surface ground. After a hole 15 is drilled or dug out, a thermocouple 16 is placed in the hole, near the bottom thereof and connected by an appropriate conductor 17 to a milli-volt meter 18, which is adapted to detect variations in voltage generated by thermocouple 16 in response to changes in temperature of the surrounding soil, and to read those voltages as temperature measurements. It is to be understood that meter 18 may be either the detachable kind, whereby it may be successively connected to a plurality of thermocouples 16, or it may be of the recording type and connected to only one thermocouple 16 for an extended period of time.

The hole is then partially filled with a uniform conducting medium, such as sand 19, up to approximately one-third of the distance from the bottom of the hole.

The purpose of sand 19 is to provide a uniform conducting medium in the hole. The remainder of the hole is then filled with soil 20 which may have been previously removed from the hole. Thereafter, the conducting medium surrounding thermocouple 16 is allowed to come to a temperature equilibrium with adjacent soil.

The practice of the present invention was carried out in one oil field which had well bores 25, 26 and 27 spaced apart in the pattern shown in FIG. 1, which well bores extended downwardly into the hydrocarbon bearing formation, the depth of which in this instance was about 115 feet.

Thereafter, a plurality of holes 15 were dug into the surface ground overlying the hydrocarbon bearing formation at spaced apart points in the area generally extending between the well bores as shown in FIG. 1, which holes 15 were of the type shown in FIG. 2, with thermocouples installed therein and connected to milli-vote meters 18.

Thereafter, a heat movement was initiated in the hydrocarbon bearing formation by the injection of approximately 5,000 barrels of water, as steam, down through well bore 26, and a similar quantity of water, as steam, down through well bore 25. During this injection and for a period of time thereafter, the milli-vote meters were monitored at periodic time intervals. After a period of time, the various meters provided the temperature readouts shown in FIG. 1. The highest temperatures were adjacent to well bores and 26 with somewhat reduced temperatures shown therebetween. However, the temperatures declined as readings were taken toard bore 27, thus indicating the extent of the movement of heat in the formation. These readings can be taken at time intervals such as daily, weekly, bi-weekly or the like.

The same procedure can be used for an in-situ combustion project to trace the movement of the combustion front through a pattern.

The foregoing method is inexpensive to perform and can be carried out with a minimum of equipment. It provides a means whereby a check can be maintained on the amount of heat injected and the location of the heat in the formation. It also provides a means for controlling the flow of heat in a heat movement. If, for example, it is discovered by this invention that the heat movement is proceeding in an unwanted direction, then certain wells may be closed in and other wells opened up to cause the heat movement to proceed in a different direction.

While the invention has been described with respect to three wells, it is to be understood that the invention may be carried out over a formation having any number of wells having any spacing pattern, with thermocouples spaced in all directions with respect to any one well or location.

Further modifications may be made in the invention as particularly described without departing from the scope thereof. Accordingly, the foregoing description is to be construed as illustratively only and is not to be construed as a limitation upon the invention as defined in the following claims.

What is claimed is:

1. The method of detecting the movement of heat in a subterranean hydrocarbon bearing formation during a thermal recovery process, said method comprising the steps of:

instituting a heat movement in said hydrocarbon bearing formation;

and monitoring changes in temperature of portions of the overburden of said formation at a plurality of monitoring points laterally spaced apart from and above the point of initiation of said heat movement as an indication of the extent of movement of said heat.

2. The method as claimed in claim 1 wherein said monitoring included the steps of:

contacting a plurality of thermocouples in heat exchange relationship with said overburden at said monitoring points;

and reading out variations in electrical voltage produced by said thermocouples in response to changes in the temperature of said overburden during said heat movement as indications of the movement of said heat.

3. The method for determining the extent of areal invasion of heat in a subterranean hydrocarbon bearing formation, said method comprising the steps of:

initiating a heat movement in said hydrocarbon bearing formation;

and monitoring changes in temperature of portions of another formation spaced above said hydrocarbon bearing formation at a plurality of monitoring points in said other formation and laterally spaced apart from the point of initiation of said heat movement as an indication of the extent of areal movement of said heat.

4. The method for determining the extent of areal invasion of heat in a subterranean hydrocarbon bearing formation, said method comprising the steps of:

initiating a heat movement in said hydrocarbon bearing formation;

and monitoring changes in temperature of portions of the surface ground above said hydrocarbon bearing formation at a plurality of monitoring points laterally spaced apart from the point of initiation of said heat movement as an indication of the extent of areal movement of said heat.

5. The method as claimed in claim 4 wherein said monitoring includes the steps of:

contacting a plurality of thermocouples in heat exchange relationship With said surface ground at said monitoring points;

and reading out variations in electrical voltage produced by said thermocouples in response to changes in the temperature of said surface ground during said heat movement as indications of the movement of said heat.

6. The method as claimed in claim 5 wherein said thermocouples were contacted with surface ground by the steps of:

digging holes from the surface into said ground;

installing said thermocouples near the bottoms of said holes;

and at least partially filling said holes.

7. The method as claimed in claim 6 wherein:

the bottom portions of said holes surrounding said thermocouples are filled with a generally uniform conducting medium;

and the medium is allowed to come to a temperature equilibrium with the adjacent ground.

8. The method as claimed in claim 7 wherein:

said holes are about four feet in depth.

9. The method as claimed in claim 7 wherein:

voltages produced by said thermocouples are monitored at periodic time intervals to determine the temperature changes of the earth near the ground surface.

10. The method for determining the extent of areal invasion of heat in a subterranean hydrocarbon bearing formation, said method comprising the steps of:

initiating a heat movement in said hydrocarbon bearing formation between at least tWo spaced apart well bores drilled into said formation;

digging a plurality of holes into the surface ground overlying said hydrocarbon bearing formation at spaced apart points in the area generally extending between said well bores;

installing a thermocouple near the bottom of each of said holes in heat exchange relationship with the adjacent ground;

and reading out variations in electrical voltage produced by said thermocouples in response to changes in the temperature of said surface ground as indications of the movement of said heat in said hydrocarbon bearing formation between said well bores.

References Cited UNITED STATES PATENTS 2,994,377 8/1961 Trantham 166l1 3,031,762 5/1962 Parker 166-4 3,172,467 3/1965 Trantham et al. 16611 JAMES J. GILL, Primary Examiner H. GOLDSTEIN, Assistant Examiner US. or. X.R. 166-251, 25a 

